U.S. Pat. No. 5,613,421, the disclosure of which is incorporated herein by reference, describers a rod-less cylinder in the form of a tube with a piston slidably received therein. The piston is adapted to move a carriage member of a rectangular shape that is located on the outer periphery of the tube. Movement of the piston within the cylinder is controlled by air pressure and a detecting sensor detects movement of the piston.